1. Field of the Disclosure
Embodiments disclosed herein relate generally to an activation system for a drilling apparatus. In particular, embodiments disclosed herein relate to an activation mechanism of a drilling apparatus to selectively open and close multiple cutter blocks of the drilling apparatus.
2. Background Art
In the drilling of oil and gas wells, concentric casing strings may be installed and cemented in the borehole as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas may be reduced. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it may be desirable to enlarge the borehole below the terminal end of the previously cased borehole. In “hole enlargement while drilling” operations (“HEWD”), the borehole is enlarged to provide a larger annular area for subsequently installing and cementing a larger casing string. Accordingly, by enlarging the borehole below the previously cased borehole, the bottom of the formation may be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly, either through a cased borehole or in conjunction with expandable casing to enlarge the borehole. One such method involves the use of expandable cutter blocks, which has basically two operative states. A closed or collapsed state may be configured where the diameter of the tool is sufficiently small to allow the tool to pass through the existing cased borehole, while an open or partly expanded state may be configured where one or more arms with cutters on the ends thereof extend from the body of the tool. In the latter position, the cutter blocks enlarge the borehole diameter as the tool is rotated and lowered in the borehole. During HEWD operations, depending upon operational requirements of the drilling assembly, cutter blocks may be extended or retracted while the assembly is downhole.
Movement of the cutter blocks typically involves manipulating a sleeve that is used to open or close ports to allow fluid to activate and expand the cutter blocks. In certain prior art applications, the sleeve is held in place with shear pins, and a ball drop device may be used to shear the pins by increasing pressure in the tool to move the sleeve and open the cutter block activation ports. However, once the pins are sheared, the tool stays open for the duration of the drilling interval as long as there is pressure in the tool bore. Therefore, such a configuration may only allow one open cycle. This is also applicable to other tools which may be expanded, including but not limited to, cutting tools, spearing tools, and expandable stabilizers.
In HEWD operations, the weight on the cutter blocks and the weight on the drill bit may vary depending upon the type of formation in which the bit and cutter blocks are in at any given time. For example, because the cutter blocks may be located up to 60 feet away from the distal end of the drillstring (upon which the drill bit is attached), the drill bit may be in a softer formation while the cutter blocks are in a harder formation. In this case, the cutter blocks may carry excessive amounts of weight, which may cause cutters on the cutter blocks to wear prematurely. As a result, the rate of penetration through the formation slows down. Currently, warning information may be provided to the operator prior to the drilling operation showing particular intervals in the formation that have an increased hardness. This requires preliminary well information to be obtained prior to the drilling operation. From this information, the operator then knows to pass through that interval with care and ease up on the weight on the reamer in order to not wear the cutter blocks prematurely.
Accordingly, there exists a need for an apparatus and method to compensate for differences in weight on the drill bit and cutter blocks to prevent premature wear of the cutter blocks while maintaining a normal and adequate rate of penetration (“ROP”) through the formation.